1. Field of the Invention
The present invention generally relates to an apparatus for filtering noise in a signal, and more particularly, to an apparatus for filtering sample-based impulse noise and line-based impulse noise in a signal.
2. Description of Related Art
Generally speaking, noise (for example, impulse noise) is usually carried by a signal when the signal is transmitted or converted in a video device. However, signal distortion may be caused by such noise and accordingly the image outputted from the video device may be distorted as well.
Conventionally, impulse noise in a signal is usually filtered out through a nullity method or a limit method. The nullity method is to reduce a signal to null when an impulse noise is detected in the signal, so as to reduce the affection of the impulse noise. In addition, the limit method is to limit a signal within a specific range when an impulse noise is detected in the signal, so as to reduce the affection of the impulse noise.
Impulse noise in a signal can be effectively filtered out through foregoing methods. However, an impulse noise further includes a short impulse noise and a long impulse noise. Because the long impulse noise exists for a longer time, if foregoing methods are adopted for filtering the long impulse noise, the characteristic of the signal itself may be changed as well (i.e., the signal containing the long impulse noise is also nullified or limited), and accordingly image distortion may be caused. Besides, if the impulse noise interferes with a timing signal of a video image and cannot be filtered effectively at a receiving end, the image outputted from the video device will be seriously distorted.